Priority of Switzerland patent application serial no. 1379/85-8, filed Mar. 30, 1985, is claimed through PCT International Application No. PCT/CH85/00099, filed Jun. 17, 1985, under 35 U.S.C. xc2xa7xc2xa7120/365.
The present invention has as its object a process for obtaining DNA, RNA, peptides, polypeptides, or proteins, through use of transformed host cells containing genes capable of expressing these RNAs, peptides, polypeptides, or proteins; that is to say, by utilization of recombinant DNA technique.
The invention aims in particular at the production of stochastic genes or fragments of stochastic genes in a fashion to permit obtaining simultaneously, after transcription and translation of these genes, a very large number (on the order of at least 10,000) of completely new proteins, in the presence of host cells (bacterial or eukaryotic) containing these genes respectively capable of expressing these proteins, and to carry out thereafter a selection or screen among the said clones, in order to determine which of them produce proteins with desired properties, for example, structural, enzymatic, catalytic, antigenic, pharmacologic, or properties of liganding, and more generally, chemical, biochemical, biological, etc. properties.
The invention also has as its aim procedures to obtain, sequences of DNA or RNA with utilizable-properties notably chemical, biochemical, or biological properties.
It is clear, therefore, that the invention is open to a very large number of applications in very many areas of science, industry, and medicine.
The process for production of peptides or polypeptides according to the invention is characterized in that one produces simultaneously, in the same medium, genes which are at least partially composed of synthetic stochastic polynucleotides, that one introduces the genes thus obtained into host cells, that one cultivates simultaneously the independent clones of the transformed host cells containing these genes in such a manner so as to clone the stochastic genes and to obtain the production of the proteins expressed by each of these stochastic genes, that one carries out selection and/or screening of the clones of transformed host cells in a manner to identify those clones producing peptides or polypeptides having at least one desired activity, that one thereafter isolates the clones thus identified and that one cultivates them to produce at least one peptide or polypeptide having the said property.
In a first mode of carrying out this process, stochastic genes are produced by stochastic copolymerization of the four kinds of deoxyphosphonucleotides, A, C, G and T from the two ends of an initially linearized expression vector, followed by formation of cohesive ends in such a fashion as to form a stochastic first strand of DNA constituted by a molecule of expression vector possessing two stochastic sequences whose 3xe2x80x2 ends are complementary, followed by the synthesis of the second strand of the stochastic DNA.
In a second mode of carrying out this process, stochastic genes are produced by copolymerization of oligonucleotides without cohesive ends, in a manner to form fragments of stochastic DNA, followed by ligation of these fragments to a previously linearized expression vector.
The expression vector can be a plasmid, notably a bacterial plasmid. Excellent results have been obtained using the plasmid pUC8 as the expression vector.
The expression vector can also be viral DNA or a hybrid of plasmid and viral DNA.
The host cells can be prokaryotic cells such as HB 101 and C 600, or eukaryotic cells.
When utilizing the procedure according to the second mode mentioned above, it is possible to utilize oligonucleotides which for a group of palindromic octamers.
Particularly good results are obtained by utilizing the following group of palindromic octamers:
5xe2x80x2 GGAAT7CC 3xe2x80x2
5xe2x80x2 GGTCGACC 3xe2x80x2
5xe2x80x2 CAAGCTTG 3xe2x80x2
5xe2x80x2 CCATATGG 3xe2x80x2
5xe2x80x2 CATCGATG 3xe2x80x2
It is also possible to use oligonucleotides which form a group of palindromic heptamers.
Very good results are obtained utilizing the following group of palindromic heptamers:
5xe2x80x2 XTCGCGA 3xe2x80x2
5xe2x80x2 XCTGCAG 3xe2x80x2
5xe2x80x2 RGGTACC 3xe2x80x2
where X=A, G, C, or T, and R=A or T
According to a method to utilize these procedures which is particularly advantageous, one isolates and purifies the transforming DNA of the plasmids from a culture of independent clones of the transformed host cells obtained by following the procedures above, then the purified DNA is cut by at least one restriction enzyme corresponding to specific enzymatic cutting site present in the palindromic octamers or heptamers but absent from the expression vector which was utilized; this cutting is followed by inactivation of the restriction enzyme, then one simultaneously treats the ensemble of linearized stochastic DNA fragments thus obtained with T4 DNA ligase, in such a manner to create a new ensemble of DNA containing new stochastic sequences, this new ensemble can therefore contain a number of stochastic genes larger than the number of genes in the initial ensemble. One then utilizes this new ensemble of transforming DNA to transform the host cells and clone these genes, and finally utilizes screening and/or selection and isolates the new clones of transformed host cells and finally these are cultivated to produce at least one peptide or polypeptide, for example, a new protein.
The property serving as the criterion for selection of the clones of host cells can be the capacity of the peptides or polypeptides, produced by a given clone, to catalyze a given chemical reaction.
For instance, for the production of several peptides and/or polypeptides, the said property can be the capacity to catalyze a sequence of reactions leading from an initial group of chemical compounds to at least one target compound.
With the aim of producing an ensemble constituted by a plurality of peptides and polypeptides which are reflexively autocatalytic, the said property can be the capacity to catalyze the synthesis of the same ensemble from amino acids and/or oligopeptides in an appropriate milieu.
The said property can also be the capacity to modify selectively the biological or chemical properties of a given compound, for example, the capacity to selectively modify the catalytic activity of a polypeptide.
The said property can also be the capacity to stimulate, inhibit, or modify at least one biological function of at least one biologically active compound, chosen, for example, among the hormones, neurotransmitters, adhesion factors, growth factors, and specific regulators of DNA replication and/or transcription and/or translation of RNA.
The said property can equally be the capacity of the peptide or polypeptide to bind to a given ligand.
The invention also has as its object the use of the peptide or polypeptide obtained by the process specified above, for the detection and/or the titration of a liquid.
According to a particularly advantageous mode of carrying out the invention, the criterion for selection of the clones of transformed host cells is the capacity of these peptides or polypeptides to simulate or modify the effects of a biologically active molecule, for example, a protein, and screening and/or selection for clones of transformed host cells producing at least one peptide or polypeptide having this property, is carried out by preparing antibodies against the active molecule, then utilizing these antibodies after their purification, to identify the clones containing this peptide or polypeptide, then by cultivating the clones thus identified, separating and purifying the peptide or polypeptide produced by these clones, and finally by submitting the peptide or polypeptide to an in vitro assay to verify that it has the capacity to simulate or modify the effects of the said molecule.
According to another mode of carrying out the process according to the invention, the property serving as the criterion of selection is that of having at least one epitope similar to one of the epitopes of a given antigen.
The invention carries over to obtaining polypeptides by the process specified above and utilizable as chemotherapeutically active substances.
In particular, in the case where the said antigen is EGF, the invention permits obtaining polypeptides usable for chemotherapeutic treatment of epitheliomas.
According to a variant of the procedure, one identifies and isolates the clones of transformed host cells producing peptides or polypeptides having the property desired, by affinity chromatography against antibodies corresponding to a protein expressed by the natural part of the DNA hybrid.
For example, in the case where the natural part of the hybrid DNA contains a gene expressing xcex2-galactosidase, one can advantageously identify and isolates the said clones of transformed host cells by affinity chromatography against anti-xcex2-galactosidase antibodies. After expression and purification of hybrid peptides or polypeptides, one can separate and isolate their novel parts.
The invention also applies to a use of the process specified above for the preparation of a vaccine; the application is characterized by the fact that antibodies against the pathogenic agent are isolated, for example, antibodies formed after injection of the pathogenic agent in the body of an animal capable of forming antibodies against this agent, and these antibodies are used to identify the clones producing at least one protein having at least one epitope similar to one of the epitopes of the pathogenic agent, the transformed host cell corresponding to these clones are cultured to produce these proteins, this protein is isolated and purified from the clones of cells, then this protein is used for the production of a vaccine against the pathogenic agent.
For example in order to prepare an anti-HVB vaccine, one can extract and purify at least one capsid protein of the HVB virus, inject this protein into an animal capable of forming antibodies against this protein having at least one epitope similar to one of the epitopes of the HVB virus, then cultivate the clones of transformed host cells corresponding to these clones in a manner to produce this protein, isolate and purify the protein from culture of these clones of cells and utilize the protein for the production of an anti-HVB vaccine.
According to an advantageous mode of carrying out the process according to the invention, the host cells consist in bacteria such as Escherichia coli whose genome contains neither the natural gene expressing xcex2-galactosidase, nor the EBG gene, that is to say, Zxe2x88x92, EBG-E. coli. The transformed cells are cultured in the presence of X gal and the indicator 1PTG in the medium, and cells positive for xcex2-galactosidase functions are detected; thereafter, the transforming DNA is transplanted into an appropriate clone of host cells for large scale culture to produce at least one peptide or polypeptide. The property serving as the criterion for selection of the transformed host cells can also be the capacity of the polypeptides or proteins produced by the culture of these clones to bind to a given compound.
This compound can be in particular chosen advantageously among peptides, polypeptides, and proteins, notably among proteins regulating the transcription activity of DNA.
On the other hand, the said compound can also be chosen among DNA and RNA sequences.
The invention has also as its object those proteins which are obtained in the case where the property serving as criterion of selection of the clones of transformed host cells consist in the capacity of these proteins to bind to regulatory proteins controlling transcription activity of the DNA, or else to DNA and RNA sequences.
The invention has, in addition, as an object, the use of a protein which is obtained in the first particular case above mentioned, as a cis-regulatory sequence controlling replication or transcription of a neighboring DNA sequence.
On the other hand, the aim of the invention also includes utilization of proteins obtained in the second case mentioned to modify the properties of transcription or replication of a sequence of DNA, in a cell containing the sequence of DNA, and expressing this protein.
The invention has as its object as well as a process of production of DNA, characterized by simultaneous production in the same medium, of genes at least partially composed of stochastic synthetic polynucleotides, in that the genes thus obtained are introduced into host cells to produce an ensemble of transformed host cells, in that screening and/or selection on this ensemble is carried out to identify those host cells containing in their genome stochastic sequences of DNA having at least one desired property, and finally, in that the DNA from the clones of host cells thus identified is isolated.
The invention further has as its object a procedure to produce RNA, characterized by simultaneous production in the same medium, of genes at least partially composed of stochastic synthetic polynucleotides, in that the genes thus obtained are introduced into host cells to produce an ensemble of transformed host cells, in that the host cells so produced are cultivated simultaneously, and screening and/or selection of this ensemble is carried out in a manner to identify those host cells containing stochastic sequences of RNA having at least one desired property, and in that the RNA is isolated from the host cells thus identified. The said property can be the capacity to bind a given compound, which might be, for example, a peptide or polypeptide or protein, or also the capacity to catalyze a given chemical reaction, or the capacity to be a transfer RNA.
Now the process according to the invention will be described in more details, as well as some of its applications, with reference to non-limitative embodiments.
First we shall describe particularly useful procedures to carry out the synthesis of stochastic genes, and the introduction of those genes in bacteria to produce clones of transformed bacteria.